bookmarks are geting lost randomly

I have been trying to determine what is causing it, but so far, I have failed to do so. Unfortunatelly, I have no extra time to go deeper into this problem and what I got is not enough for a bugzilla report, therefore I decided to at least report it here..

From time to time (aprox. every other day), some of my bookmarks get lost randomly. With no crash experiences, ff is always properly closed before computer shutdown, disk is working fine, etc. However random lines in the bookmarks.html file sometimes change from this:

<DT><A HREF="http://www.mediawiki.org/wiki/Special:Watchlist" ADD_DATE="1182894227" LAST_VISIT="1191549534" ICON="data:image/x-icon;base64,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" LAST_CHARSET="UTF-8" ID="rdf:#$P8i71">MediaWiki - Watchlist</A>

into this:

<DT><A HREF="http://www.mediawiki.org/wiki/Special:Watchlist" ADD_DATE="1182894227" LAST_VISIT="1191549534" ICON="data:image/x-icon;base64,AAABAAEAEBAAAAEACABoBQAAFgAAACgAAAAQAAAAIAAAAAEACAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABrKQIAbi4IAGM8HgBlPiAAYUEjAGFGJwBeRykAakgsAFl2aAANdZEAoXpjABFyqAAPdKYAEXegAKx6awCkiHQAD3zMAA+AzQATis0AFZbDABSUygC3mIcAFprUALugkAAUn9gAsaKZALKlmAAQoOAAFaPcAMCnlwAYrNkAoq6mAA+s5gAWr98AB7HiABCv5QAoucoAorOsABez4QAVtOQACLviAJW4tQAWv9cAPb/KABi55QAMt+8AGLvkABG66QDNuKwAoLu4ABm86QAOweQACcDoAAG/7wAXv+gAB8DwAEzB1gAlxd4ACMflAAzB8gAQyOUAI8PoACzK1wCEwcwAt8C8AA/J6QAPxvAAg8XJAB3M4QAGx/QACMX4AA7J7gAKzO0AFs7lACXO4gAVy+8ALcznAAzO8AAZ0OgAHM3tADrM5AAkzukAHdHnABLO8gAi0uUAINHoABLR7wAY0+kAMdHmABbU6gAk0+cAJNLpABXU6wAQ1esAF9TrAD3Q5gAd1OoACtTxACjT6QAW1ewAIdXoABXV7gAT1u0AHtjmADTV5gAP1fQAF9T0AGzQ3QAd1u8AEdX2ABvV9QAv2OwANNjtAIbS2wAP4fEAMd/pANbQygAb4PAATNjuAI7U4QCl2eAAq9vbAJPZ6ACV2ucA39fTAKnd5ACt3ecAq+DtAOrg3ACz4u4A5+HdAOrj3gDu5eEA5+noAOPy9AD08+wA8/LwAPby8ADk9PYA6fT2AOP2+gD59fQA6vf5APj48wD4/P0A+fz9APn9/QD8/fwA/v38APz9/QD7/f4A/v79AP7+/gD//v4A/f7/AP///wAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAi{wioeows{[{uacs{[{eousies{[{usm{ciuuq{oogayeocousiqoeocomocquocmaciimeseo{[{usm{ciuuq{oooasceousamomycosocomoSeamMeeiaoaesoaesuseam_syoaesomycosusiqoeomemcesemceeeeeoyqyqyoossoaoqyusuuqsAyqscmaciimeseo{[]mauiume{cMycosaQiooecmacacieKey{qmaIE{uymascsomm{cqmqc}ma{usm{ciuuq{oooasceo}wu}o}}cow/co}oVmu_mu}couusoutw}ruymwzouuso}}sourmzoumuonwgmceoeefowvywpowsowoqyuwwusb0=knjwokonseo~[otvotn}gMnw}uscmioycoooyulj[m{}w}asczmnkx&lt;zfnhwsowiu|vzooy{geu~smnl}sosokmosgmn]wlmwoulwoaeswsu}_sy&gt;gtwo|owsivoowog}ws~}yx?wqossoaos{www7ywgWoyqcnucm}}fsgoz[wrmzwj}uuzo?ucouu|?woome}fmwuvmkomoxqwgmucmwcmieou}cammycos_us_usiqoe_acowe_wsyyyqgeu}qqyquqwqyyquwgaesage}iigigamuesoaue_ae_usm=jt|qww_gzGwsG}swun}zclol}cwn{omu:owuc~Mediaw{oid%wgug{|{wu}s~/kds%2flycostr}t~=sfoog}gvu|~ow/wo{x}}ye&gt;osw?w}?sxewyuozwewgnnos}ct}wv|yt_}csur7wtru|}{t~osovg}q}w=95;571q{}}f}vm}l}vq57w72v73wfaygoo?vvito~ooooe?~oywo~fcmvcg}fgggggfcmow_bosoes}gfgggggow_uyqe}csoaegga_wke}qsuswysuyuoqqyquqwqyygga_sie}qqyuuwwqxyoga_ji}}sv3s7}{wgglqsyywiswqv}q~wrouki}yz~w_cwwqunucl}7wwuzq{yo}ii{}yo}kui}v{}mo}~umww}yo}nmo}w{ykmbo|o{mo{[mzgwc{mkm}y/fou}{ozwozm}{kz|wk]mekokmoow{~nmiL~uy|ykwmn;ktm0g~auvozbjwuq{oooi{kmo}{imomyko{okomo{mimmmmigoaesoaesuseam_syoaesomycosusiqoeososowsyyyqowqossoaoqyusuuqsACouuomqcmaciimeseo{[]macaoiw_{zq~sMT?7w|f{roml?" ID="rdf:#$aI5M2">oo/~mpad/content?nu~~mixuv=7o~ut~ooz{}|&gt;s{?uw~itoomnwimow{oo?{le{oshuuy~|m=[tw}ml{wsol~ks|6f}}=wyvle~f_nuum=

This weird rubish usually continues over a few original lines. Then the rubish stops and bookmarks continue. The bookmarks.html file size does not change much, but since some parts of the file are replaced with the funny stuff, some of my bookmarks get lost. If I start ff and close it again, the bookmarks.html file is "fixed" by removing all the bad stuff. After a few days without bookmarks restoring, all my bookmarks are reduced into a handful od links.

Since the suff is not proper base64, I assume some buffer is overflowing or the memory is otherwise being corrupted before the bookmarks file is saved.

Installed extensions: Clipping, CSSViewer, DOM Inspector, Html Validator, Mouse Gestures, SearchStatus. All of them updated to latest versions.

Note: I am running the Firefox Portable version from a usb flash disk. The usb is, however, not the problem, because, all my other portable applications work fine. I never unplug the usb before the data are flushed properly, etc.

Any help, suggestions? Please, note that I have already tried to reproduce this for bugzilla filling, therefore, I have already made sure about common things like:
- firefox does not crashes, the problem is elsewhere.
- the usb disk is never being improperly unplugged, the problem is elsewhere.
- the usb disk is not malfunctioning, the problem is elsewhere.

Thanks.