Computer slows or freezes and displays high memory usage message firefox + thunderbird

Question

When surfing between websites, the computer screen slows or freezes. I hit the return key and the new page can take 2-3 minutes to come up. The screen shows a message that there is high memory use on firefox, and also thunderbird when loading new incoming emails. The internet files are on C so here is a defrag report from 6.7.2011. I hope this helps your diagnosis.
Volume (C:)
Volume size = 29.29 GB
Cluster size = 4 KB
Used space = 7.73 GB
Free space = 21.57 GB
Percent free space = 73 %
Volume fragmentation
Total fragmentation = 13 %
File fragmentation = 27 %
Free space fragmentation = 0 %
File fragmentation
Total files = 31,551
Average file size = 364 KB
Total fragmented files = 4
Total excess fragments = 21,222
Average fragments per file = 1.67
Pagefile fragmentation
Pagefile size = 395 MB
Total fragments = 2
Folder fragmentation
Total folders = 3,093
Fragmented folders = 1
Excess folder fragments = 0
Master File Table (MFT) fragmentation
Total MFT size = 48 MB
MFT record count = 35,026
Percent MFT in use = 71 %
Total MFT fragments = 3
Fragments File Size Files that cannot be defragmented
7,684 804 MB \Documents and Settings\cameron\Application Data\Thunderbird\Profiles\duo7ne8y.default\Mail\mailbox.aon.at\Inbox
13,535 958 MB \Documents and Settings\cameron\Application Data\Thunderbird\Profiles\duo7ne8y.default\Mail\mailbox.aon.at\Trash

Answer 1

@ kmrupam: 3.40Ghz
@ cor-el disabling hardware acceleration didn't help unfortunately.
Thanks
Simon