Firefox 33.0 lags in text typing/ selecting/ deleting & switching tabs

Question

After an automatic update from FF 32.0.3 to FF 33.0 on 17 Oct 2014, there had been a severe browser lag. Each user action or input results in a lag lasting 1–5 secs each, making the browser very difficult & unpleasant to use.
<ul>
<li><b>Typing Text:</b> 1–2 secs before each letter appears</li>
<li><b>Highlighting Text (self-typed & web-rendered text):</b> 2–3 secs before desired text is highlighted, & only partially (eg. For "impossible", can only highlight "imposs" or "ssible")</li>
<li><b>Deleting Text: </b> 1–2 secs before each letter gets deleted</li>
<li><b>Switching Between Tabs:</b> 2–5 secs for switch</li>
<li><b>Webpage Scrolling:</b> 1–2 secs for each turn (for mouse wheel) or down-swipe (for touchpad)</li>
</ul>
All of the above issues occur everytime despite system restart, having only 1–2 tabs open, & even when FF is the only application running. I have not encountered the aforementioned problems in FF 32.0.3 & earlier FF versions, or in other browsers.
Other than FF being automatically updated to FF 33.0 on 17 Oct 2014, there was no other change (ie. no application install/ uninstall, no Windows update) that day or the preceding few days.
The lag disappears if FF 33.0 is run in safe mode with all add-ons disabled. But testing with add-ons disabled one by one does not isolate which add-on (if any) might be involved.
<ul>
<li><b>Laptop:</b> Lenovo IdeaPad Y460</li>
<li><b>OS:</b> Windows 7 SP 1</li>
<li><b>Display Adapters:</b> ATI Mobility Radeon HD5650 (driver: 8.702.5.0 latest version), Intel HD Graphics (driver: 8.702.5.0 latest version)</li>
<li><b>Firefox User Experience:</b> FF 33.0 (very bad lag), FF 32.0.3 & earlier (all function ok)</li>
<li><b>Browser Add-ons & Plugins:</b> All latest versions</li>
</ul>
<b>What I eventually did</b> (a few days before reporting here after registering a user account):
Since I was unable to resolve the problem, I performed a successful system restore, but the rolled-back browser (FF 32.0.3) was unable to launch (error code: "can't load XPCOM"). Subsequently, I resorted to installing a fresh copy of FF 32.0.3.
<hr>
Since 17/18 Oct 2014, I have encountered a couple of reports about similar lag issues in FF 33.0 (& possibly since FF 32.0.* for some users). The collective symptoms & feedback suggest that it is probably not add-ons causing the issue, but some newly-created <b>incompatibility or conflict with certain (or combinations of) display/ graphics adapter(s)</b>. So far, the reported affected adapters that I have come across include the ATI Mobility Radeon HD5000 series, Intel HD Graphics, & NVIDIA GeForce.
The temporary workaround appears to be disabling the hardware acceleration option. But since this is not a long-term solution, I am holding off updating to FF 33.0 (again) or to the just-released FF 33.0.1, until this issue is officially recognized & resolved.
Note:- Some users with text/ tab lagging problems also reported slowness wrt video &/or flash pages, which I can't verify because I had not tested FF 33.0 on video/ flash pages before reinstalling FF 32.0.3. (The text, tab & scrolling lags are enough to keep me away from browsing anything but the most basic webpages.)
Some Feedback References (for affected users & FF developers):
<ul>
<li><b>Firefox UI is slow when typing or selecting text (after 33.0 update)</b> (Mozilla Support Forum, posts: 17 Oct–20 Oct 2014): https://support.mozilla.org/en-US/questions/1026328</li>
<li><b>Bug 1087794: Firefox 33.0 exhibits weird behavior like slow typing, flash content blinking, problems with text selection</b> (Bugzilla@Mozilla, posts: 22 Oct–23 Oct2014): https://bugzilla.mozilla.org/show_bug.cgi?id=1087794</li>
<li><b>Crippling lag since version 32</b> (Reddit, posts: 8 Oct–25 Oct 2014): https://www.reddit.com/r/firefox/comments/2iobft/crippling_lag_since_version_32</li>
<li><b>Firefox v33.0: Closing tabs or switching between tabs sometimes hangs for 30-40 seconds</b> (Reddit, posts: 23 Oct 2014): https://www.reddit.com/r/firefox/comments/2k40zx/closing_tabs_or_switching_between_tabs_sometimes</li>
</ul>
Possibly related to the same bug:-
<ul>
<li><b>YouTube slowing after update</b> (Reddit, posts: 16 Oct–18 Oct 2014): https://www.reddit.com/r/firefox/comments/2jfkap/youtube_slowing_after_update</li>
<li><b>Browser Lag (mostly when opening a tab or scrolling on webpage)</b> (Reddit, posts: 15 Oct–16 Oct 2014): https://www.reddit.com/r/firefox/comments/2jcxns/browser_lag</li>
</ul>

Answer 1

Hello,
Try disabling graphics hardware acceleration. Since this feature was added to Firefox, it has gradually improved, but there still are a few glitches.
'''[https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode Start Firefox in Safe Mode]''' {web link}
While you are in safe mode;
Type '''about:preferences'''<Enter> in the address bar
Select '''Advanced > General.'''
Look for and turn off '''Use Hardware Acceleration'''.
Poke around safe web sites. Are there any problems?
Then restart.